This project concerns the structure and function of he prokaryotic ribosome - the organelle that orchestrates protein biosynthesis. The ribosome is an ancient organelle that is central to all life and, although current knowledge and ongoing research on this system is extensive, there is almost no understanding of how it operates at the molecular level. It is proposed to use X-ray crystallographic techniques to investigate the structures of individual components of the ribosome. These include 6 ribosomal proteins, a protein/ribsomal (r) RNA complex, and a protein/rRNA/drug complex. To date, only two ribosomal protein structures are known (the C-terminal half of L7/L12, and L30), and progress on others has been slow. This reflects the difficulty in obtaining sufficient quantities of the proteins for crystallographic studies. This problem has recently been overcome by the ability to clone and express the genes for these proteins in a modified bacteriophage T7 expression system. In principle, it is now possible to study any protein of choice. Of the 6 proteins that are to be investigated, 4 have already been crystallized and structural studies initiated (L6,L9,L30 and S5). The remaining 2 have been chosen for specific reasons. L11 is known to form stable complexes with a fragment of rRNA and with the rRNA bound to the drug thiostrepton. The isolated protein and the two complexes will be crystallized and their structures determined. L14 has been predicted to have the same structural motif as that shared by L7/L12 and l30, and this will be investigated by crystallographic analysis. All proteins will be cloned from the thermophilic organism Bacillus stearothermophilus since these have been shown to crystallize most readily. It is absolutely vital to an organism that the ribosome functions correctly. These studies represent an important step towards an understanding of the ribosomal mechanisms at the molecular level, and will provide insights into the causes behind their malfunction. It is not surprising that many drugs and antibiotics operate by binding to and disrupting the ribosomal machinery. This work will provide a detailed view of such an interaction. It will also provide important and much needed information on how proteins interact with RNA. Finally, the studies of L14 will yield information not only on the evolution of the ribosome, but also on the important subject of protein folding.